Known in the art is steel consisting of 0.13% by weight of carbon, 0.15-0.30% by weight of silicon, 0.30-0.55% by weight of manganese, 1-1.5% by weight of chromium, 1.0-1.6% by weight of nickel, 0.5-0.7% by weight of molybdenum, 0.01-0.10% by weight of vanadium, 0.02-0.04% by weight of cerium, sulphur and phosphorus in a quantity of less than or equal to 0.020% by weight, iron- the balance. Such steel possesses high mechanical properties (yield strength of 50 kg/mm.sup.2); however, it is prone to embrittlement under the action of neutron radiation (transition embrittlement temperature T.sub.k increases by 120.degree.-160.degree. C. with neutron fluence of about 1.10.sup.20 neutr./cm.sup.2). In addition, the prior art steel cannot be used for making structural members having a wall thickness exceeding 400 mm due to insufficient hardening depth.
Known in the art is also steel consisting of 0.11-0.25% by weight of carbon, 0.17-0.37% by weight of silicon, 0.3-0.6% by weight of manganese, 2-3% by weight of chromium, 0.6-0.8% by weight of molybdenum, 0.25-0.35% by weight of vanadium, a quantity of sulphur and phosphorus less than or equal to 0.025% by weight, iron- the balance. The steel exhibits high strength (yield strength equal to or less than 55 kg/mm.sup.2) and good resistance against radiation (an increase in the transition embrittlement temperature .DELTA.T.sub.k is less than or equal to 60.degree. C. with a neutron fluence of about 1.10.sup.20 neutr./cm.sup.2). This steel cannot, however, be used for the manufacture of structural members with a wall thickness exceeding 400 mm, and welding of such members is associated with difficulties because an accompanying heating at 300.degree.-350.degree. C. and immediate tempering are required after the welding.
Known in the art is steel consisting of 0.25% by weight of carbon, 0.15-0.3% by weight of silicon, 0.5-1.5% by weight of manganese, 0.4-0.7% by weight of nickel, 0.45-0.6% by weight of molybdenum, 0.04% by weight of sulphur, 0.035% by weight of phosphorus, iron- the balance. This steel features good manufacturing properties and weldability, but is characterized by low strength (yield strength equal to or less than 35 kg/mm.sup.2), is embrittled under the action of neutron radiation (.DELTA.T.sub.k =100.degree.-200.degree. C. with a fluence of neutrons of about 5.10.sup.19 neutr./cm.sup.2).
Also known in the art is steel containing 0.20% by weight of carbon, 0.020-0.3% by weight of silicon, 0.4% by weight of manganese, 1.5-2.0% by weight of chromium, 3-4% by weight of nickel, 0.45-0.60% by weight of molybdenum, 0.03% by weight of vanadium, .ltoreq.0.02% by weight of sulphur and phosphorus, iron- the balance.
This steel exhibits high strength (yield strength equal to or less than 60 kgf/mm.sup.2) and high toughness, it is good for welding. However, this steel is prone to embrittlement under heat and radiation action (.DELTA.T.sub.k =100.degree.-150.degree. C. with a fluence of neutrons of about 5.10.sup.19 neutr./cm.sup.2).
It is an object of the invention to eliminate the above disadvantages.
The main object of the invention is to provide steel to be used in the manufacture of casings of nuclear reactors which exhibits an improved resistance against the action of neutron radiation.
Another object of the invention is to provide steel which exhibits an improved hardening depth.
The invention consists in the provision of steel containing such components and in such proportions as to improve the resistance of steel against the action of neutron radiation and increase hardening depth of the steel.